The present invention relates to a latch needle for machines producing knit goods, the needle including a needle shank, a needle head and a needle latch, the needle latch being mounted in a slot of the needle shank so as to be pivotable about a latch axis which is transverse to the longitudinal axis of the needle.
In order to produce knit goods having acceptable quality, the latch needles must open and close properly during loop formation in the knitting process. In view of this consideration, the pivotable latch is guided in a close fit within the slot of the needle shank. The latch is supported by bearings and has a noucat or latch spoon which is oriented toward the tip of the hook in such a manner that, in spite of axial and radial bearing play required to render the latch easily pivotable, the noucat lies properly on the needle head when the latch is closed.
The latch can be laterally deflected, however, due to the aforementioned bearing play. Additionally, the latch can be deflected by lateral forces which act on the latch and on the needle head during loop formation. These lateral forces can originate, for example in a circular knitting machine, due to carrying of the needle during rotary movement of the needle cylinder and the dial. Wear of the latch bearing causes additional axial play which results in further lateral deflection of the latch, particularly after a longer period of operation. The result in this eventuality is that the noucat of the latch no longer lies centrally on the needle head and instead brushes against a knitting tool, the knitting tool being, for example, a sinker or transfer jack adjacent to the needle. This interferes with the pivoting movement of the needle latch, resulting in the formation of longitudinal stripes or lines in the knit product. Moreover, additional lateral wear thereby occurs on the latch.
The undesirable lateral deflection of the needle latch is frequently exacerbated by the fact that, in some latch needle designs, the needle has a reduced shank height in its frontal region adjacent the head. For example, in order to save weight, particularly for needles intended for small circular knitting machines, the shank height between the needle butt and the groove is made to be as low as possible. Due to this low shank height, the stability of the latch needle in its shank region following the head is correspondingly reduced.
During loop formation, lateral forces are generated, for example, by the product removal device. Under the influence of the lateral forces acting on the head and groove region of the needle during loop formation, the needle is moved out of its symmetrical position toward its respective needle bed wall by the required play between adjacent needle bed walls and the needle shank, and the loop forming portion of the latch needle which projects from the needle bed is also inevitably pushed elastically somewhat to the side out of its original central position. A needle latch whose noucat is no longer oriented precisely toward the tip of the hook is thus brought closer to the adjacent knitting tool, this knitting tool being, for example, the adjacent sinker or transfer jack, so that pivoting movement of the latch causes the noucat of the latch to brush against the knitting tool.
In a latch needle disclosed in German Pat. No. 3,140,386, which corresponds to U.S. Pat. No. 4,498,315, an attempt to overcome the problems discussed in the foregoing, results in a needle having a latch, that has a shaft portion terminating in a noucat, wherein the noucat of the latch is set at an angle to the plane of symmetry of the shaft of the latch. The noucat is oriented to one side of the needle shank in order to ensure that in the closed position of the latch, when the latch is pushed against the wall of the slot due to lateral forces, the noucat rests on the needle head. The noucat is oriented such that it rests on the needle head both when the latch needle is at rest and also when the latch needle is engaged in the knitting process and is therefore subject to the aforementioned lateral forces. Such latch needles have been found to be quite satisfactory in practice. However, in a desire to further reduce the needle stroke and thereby increase knitting speeds, latch needles are produced today with a very short latch motion, with the length of the latch sometimes being only 2 mm including the noucat. With such short latches, however, limitations in manufacturing technology prevent the noucat of this type of needle from being placed at angles which would be required under these conditions.